Studies of chemical disposition are designed to provide both applied knowledge of the fate of chemicals in the intact animal in support of toxicity tests conducted by the National Toxicology Program and basic knowledge of mechanisms of chemical toxicity. Thus, objectives of these studies are two fold. Each study is designed to address those physical and chemical properties unique to the compound studied as well as to provide data which will permit structural characterization of the respective chemical class. Each study is also designed to address the impact of one or more factors such as dose, age, sex or route of exposure on the toxicity of the chemical(s) studied and the significance of this data to assessments of human health risks. One of the chemicals of current interest, oxymethylone, is a synthetic anabolic steroid structurally related to testosterone. This steroid is used therapeutically to treat certain types of anemia, but has been used recreationally by body builders to enhance muscle mass and endurance. Use of oxymetholone has been associated with incidences of hepatic toxicity and an increased incidence of tumors. Studies of the disposition and metabolism of this compound have established that it is rapidly absorbed from the gastrointestinal tract, metabolized and eliminated with a half-life of approximately 11 h, This compound is highly bound to plasma proteins and accumulates in blood with repeat dosing for up to seven daily doses when blood concentrations plateau. Another compound, currently under study is ethoxyquin, a derivative of quinoline a known hepatocarcinogen in rats. Ethoxyquin is used primarily as an antioxident in animal feeds. Studies of the metabolism and disposition of this compound indicate that it is rapidly absorbed, metabolized and excreted.